TUNING PARTICULATE FILTER PERFORMANCE THROUGH SELECTIVE PLUGGING AND USE OF MULTIPLE PARTICULATE FILTERS TO REDUCE EMISSIONS AND IMPROVE THERMAL ROBUSTNESS

Description

[0001] The invention relates to exhaust aftertreatment filters for filtering exhaust from internal combustion engines, including diesel engines, comprising the features of the generic part of claim 1.

[0002] Exhaust aftertreatment filters for diesel engines are known in the prior art. The filter traps contaminant particulate present in exhaust, and in order to remove the trapped particulate, the filter is heated to bum-off the trapped contaminant particulate as gas, Accordingly, the filter is regenerable and is composed of material on which trapped contaminant particulate from the engine exhaust is removed by addition of heat. Commonly used particulate filter materials include cordierite, silicon carbide, mullite, or aluminum titanate, which are manufactured as filter elements to capture the soot and other particulate generated by the engine.

[0003] Diesel particulate filters (DPF) are subject to high temperatures during use. The design of the DPF consists of a honeycomb structure with opposing channels blocked to force exhaust gases to flow through the porous channel walls, while trapping soot. The soot (composed primarily of carbon) accumulates in the DPF and must be removed periodically. Typically, the soot is removed from the filter by oxidation reactions between carbon in the soot and either oxygen (i.e., burning) or nitrogen dioxide, both of which are constituents of the exhaust. The carbon may react with oxygen or nitrogen dioxide according to the following reactions:

        C_(s) + O_2(g) → CO_2(g)     (1)

        C_(s) + 2NO₂ → CO_2(g) + 2NO_(g)     (2)

[0004] Reaction (1) is the primary reaction that occurs during an active regeneration. Reaction (2) is the primary reaction that occurs during passive regeneration. Heat is a significant by-product of the reaction shown in Reaction (1) and, if not controlled, can cause thermal runaway of the filter, leading to fractures and/or melting of the filter and rendering it ineffective as a filter.

[0005] Although thermal runaway may be prevented by controlling the rate at which carbon is burned in the filter, nonetheless the DPF may be subject to thermal gradients caused by differential heating patterns, which also may lead to fractures. Differential heating may occur during active regeneration of the filter where carbon may be unequally distributed, either radially or axially, within the DPF. For example, carbon may be more highly distributed in the DPF at locations where the largest volume of exhaust passes through the filter (i.e., at locations where exhaust velocity is highest). These locations may exhibit a relatively high temperature during active regeneration as compared to other locations.

[0006] Although carbon distribution may be altered by modifying the design of a filter, particulate filter manufacturers are hampered by material strength issues that limit the maximum porosity that can be obtained in an extruded honeycomb structure. Filter manufacturers typically design filters that have the lowest back pressure and suitable filtration efficiency as required for a particular engine. However, ceramic filter manufacturers have difficulty designing filters that have the lowest back pressure and suitable filtration efficiency without greatly weakening the honeycomb structures. Furthermore, it is commonly believed that filtration efficiency drops precipitously with even a single unblocked or broken channel in the honeycomb structure of the filter, even though unblocked channels might lower back pressure.

[0007] Therefore, there is a need for filters having modified design characteristics in order to minimize back pressure and thermal gradients during regeneration. Furthermore, it is desirable that these modified design characteristics can be combined with control techniques to create filters that are more durable and resistant to structural damage which may occur during use of the filter (e.g., during regeneration).

[0008] Disclosed in the prior art (US-A-7,052,532) are exhaust aftertreatment filters and systems for filtering engine exhaust flowing along an axial direction. This prior art exhaust aftertreatment filter includes a plurality of flow channels comprising a plurality of wall-flow channels which are alternately sealed at downstream ends or upstream ends.

[0009] The exhaust aftertreatment filter according to WO 01/12320 A1 has in addition a plurality of flow-through channels. In this exhaust aftertreatment filter said wall segments further define a third set of channels having open flow, said third set of channels having selected positions in said filter possibly for reducing back pressure on said filter during operation while operation maintaining filtering efficiency and/or for reducing high temperature in said filter during operation while maintaining filtering efficiency and/or for increasing velocity of exhaust flow through said filter during operation while maintaining filtering efficiency.

[0010] Above mentioned exhaust aftertreatment filter is more durable and resistant to structural damage which may occur during use of the filter by way of the features of the characterizing part of claim 1.

[0011] The filter according to claim 1 includes wall segments further defining a fourth set of channels having closed downstream ends and closed upstream ends (i.e. closed channels), The closed channels are positioned in the filter in order to reduce physical damage to the periphery of the filter. To that effect the closed channels form a peripheral ring in the filter.

[0012] Preferred modifications and improvements of the exhaust aftertreatment filter according to the invention are subject matter of dependent claims 2 to 7, The main aspects of the dependent claims are discussed hereafter.

[0013] The disclosed filters may be regenerable and composed of monolithic material on which trapped contaminant particulate from the engine exhaust is removed by addition of heat. In some embodiments, the filters are composed of material comprising an axially extending filter element having wall segments extending axially between upstream and downstream ends. The wall segments may define a plurality of axial flow channels including wall-flow channels and flow-through channels. Typically, the wall segments define a first set of first wall-flow channels where the wall segments are alternately sealed to each other by a first set of plugs to define a first set of wall-flow channels closed by the plugs and having open downstream ends; and the wall segments define a set of second wall-flow channels interdigitated with the first set of flow channels and having open upstream ends, the wall segments being alternately sealed to each other by a second set of plugs closing the second set of flow channels. The wall segments further define a third set of flow-through channels positioned in the filter for modifying the performance of the filter (e.g., achieving reduced back pressure, reduced temperature, and/or increased velocity of exhaust) while maintaining adequate filtering efficiency (e.g., efficiency of at least about 95%, 90%, 85%, 80%, 75%, 70%, 60%, or 50% for soot concentrations of about 2.0 gL or less).

[0014] The number of flow-through channels may be adjusted to achieve a desired filter performance. In some embodiments, the number of flow-through channels represents at least about 1% of total channels (or at least about 2% of total channels in some embodiments) while the maintained filtering efficiency is at least about 90% (e.g., for soot concentrations of about 2.0 g/L or less). In other embodiments, the number of flow-through channels represents at least about 5% of total channels (or at least about 10% of total channels in some embodiments) while the maintained filtering efficiency is at least about 80% (e.g., for soot concentrations of about 2.0 g/L or less).

[0015] The filter may include a coating. For example, the wall segments of the filter may be coated with a coating material, which optionally may include a catalytic agent. In some embodiments of the filters, wall segments defining flow-through channels are coated with a coating material that comprises a catalytic agent. Catalytic agents may include oxidizing catalysts and reducing catalysts. Catalytic agents may include catalysts for at least one reaction selected from the group consisting of C + O₂ → CO₂ and 2NO + O₂ → 2NO₂. Catalytic agents may include noble metals (e.g., platinum, rhodium, and palladium.)

[0016] The wall segments defining the flow-through channels may have an average thickness different than an average thickness of the wall segments defining the first set of wall-flow channels or the wall segments defining the second set of wall-flow channels. In some embodiments of the filters, the wall segments defining the flow-through channels have an average thickness greater than an average thickness of the wall segments defining the first set of wall-flow channels or the wall segments defining the second set of wall-flow channels.

[0017] The flow-through channels may be distributed in the filter in any suitable arrangement. In some embodiments, the flow-through channels are distributed in the filter in a gradient, where the filter has an increasing concentration of open channels in sections located at peripheral positions in the filter as compared to sections located at central positions of the filter.

[0018] Optionally, the wall segments defining the closed channels have an average thickness greater than an average thickness of the wall segments defining the first set of wall-flow channels or the wall segments defining the second set of wall-flow channels. In further embodiments, the flow-through channels may be arranged in a ring adjacent to a peripheral ring formed by the closed channels.

[0019] The filter may be composed of any suitable material. In some embodiments, the filter is composed of a ceramic material, examples of which are cordierite, silicon carbide, mullite, and aluminum titanate. The filter may be monolithic (i.e., composed of single piece of material), or segmented (i.e., composed of multiple pieces of material bonded together).

[0020] The filters may be utilized alone or may be combined with additional components in an exhaust aftertreatment system for filtering engine exhaust flowing along an axial direction. For example, an exhaust aftertreatment system as disclosed herein may include the following components in series along an axial direction: a diesel oxidation catalyst, a first filter as disclosed herein, and optionally a second filter. This is the subject matter of claim 8.

[0021] A further interesting exhaust aftertreatment system filtering engine exhaust flowing along an axial direction may comprise at least a first filter and a second filter arranged in series along the axial direction, where the first filter is positioned upstream of the second filter and has a lower filtration efficiency than the second filter. This system is the subject matter of claim 9. At least one of set first and second filters is a filter according to any one of the claims 1 to 7.

[0022] Preferred improvements and modifications of this system are the subject matter of dependent claims 10 to 13. Many aspects thereof are discussed hereafter.

[0023] The first and second filter may be composed of a monolithic ceramic material such as cordierite, silicon carbide, mullite, and aluminum titanate (optionally having a honeycomb or ceramic bead structure). The first filter, second filter, or both filters may include a coating material that comprises a catalytic agent (e.g., an oxidizing catalyst for converting nitric oxide to nitrogen dioxide). Typically, at least one of the first and second filters includes a plurality of wall-flow channels and flow-through channels. Optionally, at least one of the first and second filters includes closed channels. The flow-through channels and closed channels, if present, may be arranged in any suitable formation, including a formation where a peripheral ring of closed channels surrounds an adjacent ring of flow-through channels.

[0024] In the disclosed systems, the first filter may be composed of a first regenerable material and the second filter may be composed of a second regenerable material that is different than the first regenerable material. For example, the first regenerable material may have a larger pore diameter than the second regenerable material. In some embodiments, the first filter is a high cell density flow-through element having a cell density of greater than 200 per square inch. In other embodiments, the first filter may be a partially plugged filter. In further embodiments, the second filter may have a high cell density (e.g., a cell density of greater than 200 per square inch), which may be higher than the first filter. (1 square inch = 6.4516 cm²)

[0025] In a preferred embodiment the wall segments defining a third set of flow channels have an average thickness greater than an average thickness of the wall segments defining the first set of flow channels or the wall segments defining the second set of flow channels.

[0026] Further, the wall segments of the first filter that define a fourth set of flow channels have closed downstream ends and closed upstream ends with this fourth set of flow channels forming a peripheral ring in the first filter.

[0027] In the disclosed systems, the first filter may have a soot filtration efficiency that is lower than the second filter. In some embodiments, the first filter has a soot filtration efficiency of at least about 50% (e.g., about 50-60% in some embodiments) and the second filter has a soot filtration efficiency of at least about 90% (or at least about 95% in some embodiments).

[0028] The disclosed systems optionally include a catalytic converter element, such as a diesel oxidation catalyst element, which may be arranged in series with the first filter and the second filter along the axial direction. The catalytic converter element may be positioned upstream of the first filter and may include an oxidizing catalyst for at least one reaction selected from the group consisting of 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; and 4C_xH_y + (4x+y)O₂ → (4x)CO₂ + (2y)H₂O (where in some embodiments x is an integer from 1-25 and y is an integer from 0-52). In some embodiments, the first filter may include an oxidizing catalyst for at least one reaction selected from the group consisting of 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; and 4C_xH_y + (4x+y)O₂ → (4x)CO₂ + (2y)H₂O (where in some embodiments x is an integer from 1-25 and y is an integer from 0-52). Optionally, the second filter may include an oxidizing catalyst for at least one reaction selected from the group consisting of 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; and 4C_xH_y + (4x+y)O₂, → (4x)CO₂ + (2y)H₂O (where in some embodiments x is an integer from 1-25 and y is an integer from 0-52).

[0029] Also disclosed are methods for manufacturing a modified exhaust aftertreatment filter for filtering engine exhaust flowing along an axial direction and having modified performance. The modified filter has a structure as described herein.

[0030] In some embodiments of the methods of manufacture, an unmodified filter is composed of regenerable material comprising an axially extending filter element having wall segments extending axially between upstream and downstream ends. The wall segments may define a plurality of axial flow channels including wall-flow channels and flow-through channels. Typically, the wall segments define a first set of first wall-flow channels where the wall segments are alternately sealed to each other by a first set of plugs to define a first set of wall-flow channels closed by the plugs and having open downstream ends; and the wall segments define a set of second wall-flow channels interdigitated with the first set of flow channels and having open upstream ends, the wall segments being alternately sealed to each other by a second set of plugs closing the second set of flow channels.

[0031] The methods of manufacture typically include selecting and removing at least one plug of the first set of plugs and the second set of plugs to provide open flow in at least one channel of the modified filter. In some embodiments, the selected plug for removal is located at a position in the unmodified filter whereby removing the plug reduces back pressure on the modified filter during operation while maintaining filtering efficiency. In other embodiments, the selected plug for removal is located at a position in the unmodified filter which is subject to relatively high temperature during operation of the unmodified filter as compared to a non-selected plug, thereby reducing the relatively high temperature during operation of the modified filter while maintaining filtering efficiency. In further embodiments, the selected plug for removal is located at a position in the unmodified filter where exhaust flow exhibits relatively low velocity during operation of the unmodified filter as compared to a position of a non-selected plug, thereby increasing the relatively low velocity during operation of the modified filter while maintaining filtering efficiency.
Also disclosed are exhaust aftertreatment filters for filtering engine exhaust prepared by the disclosed methods of manufacture. In some embodiments, the filters prepared by the methods of manufacture include a number of flow-through channels representing at least about 1% of total channels (or at least about 2% of total channels in some embodiments) while the maintained filtering efficiency of the modified filter is at least about 90% (or at least about 80% in some embodiments) (e.g., for soot concentrations of about 2.0 g/L or less).

[0032] Hereafter a preferred embodiment is explained with reference to the drawings. In the drawings:

Fig. 1

is a perspective view of an exhaust aftertreatment filter.

Fig. 2

is a sectional view of the exhaust aftertreatment filter of Figure 1.

Fig. 3

illustrates the effects on filtering efficiency (top) and filter restriction (bottom) versus percentage channels open (i,e., percentage flow-through channels) in a modified filter having a 30.48 cm (12 inch) diameter by 30.48 cm (12 inch) length with 200 cells per square inch. (1 square inch = 6.4516 cm²)

Fig. 4a

illustrates the velocity of exhaust through a filter exhibiting a parabolic flow profile. Figure 4b illustrates a potential distribution of open channels in a filter designed to increase flow at locations of relatively low exhaust velocity in view of the parabolic flow profile of Figure 4a.

Fig. 5a

illustrates the velocity of exhaust through a filter exhibiting a turning flow profile.

Fig. 5b

illustrates a potential distribution of open channels in a filter designed to increase flow at locations of relatively low exhaust velocity in view of the turning flow profile of Figure 5a.

Fig. 6a

illustrates the velocity of exhaust through a filter exhibiting a flat velocity profile.

Fig. 6b

illustrates a potential distribution of open channels in a filter designed to increase flow at locations of relatively low exhaust velocity in view of the flat flow profile of Figure 6a.

Fig. 7

illustrates two filters having sample unplugging patterns (i.e., modified filters). The sample patterns include a 2-cell (or 4-cell) peripheral ring of double-plugged channels adjacent to a 2-cell (or 4-cell) ring of flow-through channels.

Fig. 8

illustrates an exhaust aftertreatment system including a diesel oxidation catalyst (DOC) in series with a first filter element and a second filter element.

[0033] Fig. 1 shows an exhaust aftertreatment filter 10 for filtering exhaust from an internal combustion engine, such as diesel engine 12, flowing along an axial flow direction 14. Fig. 2 shows a section view of the filter of Fig. 1. The filter is composed of particulate filtration material 16, as known in the prior art, for example ceramic such as a cordierite, silicon carbide, mullite, or aluminum titanate on which trapped contaminant particulate from the engine exhaust is removed by addition of heat. The filter 10 includes wall-flow channels formed by wall segments having an upstream plug 34 or a downstream plug 36. Contaminant particulate such as soot is trapped and accumulates in the filter, which trapped contaminant particulate is burned-off during regeneration. The filter includes a filter body 18 having an outer periphery 20 surrounding a central core 22. Outer periphery 20 and central core 22 may be subject to differential thermal expansion during thermal cycling during regeneration, due to outer periphery 20 being cooler than central core 22. For example, Figure 2 shows central hot spot 24, which is hotter than outer periphery 20, and which may be more dominant at the downstream side of the filter where particulate contaminant may accumulate and clog. With or without clogging or a downstream hot spot such as 24, outer periphery 20 may run cooler than central core 22, as is known. The filter is typically mounted in a housing 26, such as a stainless steel canister, having a mat mounting material 28 surrounding the filter body and performing a number of functions including thermal resistance, dampening of vibration, and resistance to movement. The mat material is typically compressed between housing 26 and filter body 18.

[0034] The noted differential thermal expansion between hotter central core 22 and cooler outer periphery 20 may subject the filter body to separational axial tensile stress in the axial direction which in turn subjects the filter body to separational fracture and cracking, for example as shown at fracture or crack line 30 in Figure 1. It is known by catalyst and filter manufacturers that the radial compressive stress applied by pressure obtained from an expanding mat material 28 assists in reducing the fracture probability of filter body 18. However, the radial compressive stress reduces the probability of fracture along a fracture line parallel to axis 31 of the filter perpendicular to crack line 30), and does little to prevent fractures along a fracture or crack line such as 30. Furthermore, the mat material can degrade over time, resulting in loss of pressure. With larger and heavier filters and longer lifetimes, particularly for diesel particulate filters in wall-flow application versus automotive flow-through catalyst application, the noted pressure and compressive stress applied by mat material 28 will decrease more rapidly, particularly than that observed for automotive catalysts. Furthermore, an automotive catalyst can still function after cracking because of its flow-through application, whereas a contaminant particulate filter loses effectiveness if cracked because of the bypass flow path created. The filter may include a pre-stressed layer 32 bonded to filter body 18 at outer periphery 20 and is compressively axially pre-stressed in the opposite axial direction to the noted separational axial tensile stress to counteract the latter during regenerative heating.

[0035] The modified exhaust aftertreatment filters disclosed herein include a plurality of flow-through channels obtained by removing an upstream plug 34 or downstream plug 36 in what otherwise would be a wall-flow channel in an unmodified filter. The selected flow-through channels may be located at any suitable position in the modified filter and may be patterned in the filter in order to modify the performance of the filter. In some embodiments, open-flow channels may be provided at locations that are normally are subject to relatively low exhaust gas flow (e.g., locations at the outer diameter of the filter), which may result in a decreased pressure drop. The modified filters may include a percentage of open-flow channels relative to total channels that does not significantly impair filtering efficiency as illustrated in Figure 3.

[0036] For a filter subject to low speed laminar flow with a parabolic exhaust velocity distribution, channels may be opened in such a pattern that the number of the open channels is inversely related to the pipe velocity as shown in Figure 4, and according to the equation N = kl/(Velocity Profile), where N is the number of open channels within a selected area of the filter and kl is a coefficient which can be tuned to optimize the flow distribution. If a filter is located right after a fitting due to space constrain (such as an elbow or an expansion tube) and the fitting causes sudden changes of flow pathlines, channels may be opened against the velocity profile as shown in Figure 5. For fully developed turbulent flows as shown in Figure 6, the following equation may be used to determine a suitable number of open channels for a given area of the filter: N = k2/(Velocity Profile)^1/n, where N is the number of open channels within a selected area of the filter; k2 is a coefficient which can be tuned to optimize the flow distribution; and 1 < n < 2.

[0037] The modified filters typically include open-flow channels (i.e., unplugged channels). Optionally, the modified filters may include double-plugged channels (i.e., channels having both an upstream plug 34 and a downstream plug 36, as compared to a single-plug channel having only an upstream plug 34 or a downstream plug 36 and defining a wall-flow channel). The unplugged channels and double-plugged channels may be arranged in any suitable formation. Figure 7 illustrates an arrangement in filter having a peripheral ring of double-plugged channels (either 2-cells or 4-cells wide) adjacent to a ring of unplugged channels (either 2-cells or 4-cells wide). For both double-plugged and unplugged cells (optionally in a ring formation), the wall thickness may be higher than single-plugged cells. A filter having double-plugged or unplugged cells with thicker walls may be more robust to handling, regeneration thermal shock, or ringoff failures. In some embodiments of the filters, double-plugged and unplugged cells may have lesser wall porosity relative to single-plugged cells.

[0038] A variety of distributions of plugs in the filters could be used to change gas flow, particularly in combination with a series filtration approach. For example, the disclosed filters may be used in a modified diesel particulate filter design to lower engine back pressure and improve soot distribution. In some embodiments, the design includes two filter elements, where the first filter element may have lower filtration efficiency than the second filter element.

[0039] By modifying the element architecture, it may be possible to improve the soot distribution on the filter, reduce thermal gradients during an active regeneration, and increase the level of passive regeneration. In a modified diesel particulate filter design, the filter element may be broken into two or more elements with progressively increasing filtration efficiency. Commonly, DPFs have about 90% filtration efficiency. In a modified diesel particulate filter design, the filter may be separated into two separate filter elements. For example, the first filter may have a filtering efficiency on the order of 50-60%, while the second filter may have a filtration efficiency of about 90%. The reduction in filtration efficiency for the first filter may be attained by several methods. One method may be to reduce the percentage of plugged channels, either randomly, or in a specific pattern in the first filter. A second method may be to increase the pore diameter of the filter material of the first filter, thus allowing more soot particles to pass through the walls. A third method may be to use a high cell density flow-through element for the first filter (e.g., an element having a cell density greater than about 200 cells per square inch) (1 square inch = 6.4516 cm²).

[0040] Potential methods for decreasing filtration efficiency for the first filter element could be to use a high cell density flow-through element, higher pore size filters, or selective plugging of channels (partially plugged filter). The use of a partially plugged filter may be used to affect the flow distribution and temperature distribution within a modified diesel particulate filter design.

[0041] A filtration system, as shown in Figure 8, incorporates a DOC to heat the exhaust gases to burn the accumulated soot in the filters. The first filter may also incorporate a catalyst to burn hydrocarbons not burned in the DOC and to oxidize NO (nitric oxide). Optionally, the second filter may incorporate a catalyst.

[0042] Catalysts, as described herein, may include oxidation catalysts and reduction catalysts. Catalysts may include NO_x adsorbers (e.g., where x is 1 or 2). In some embodiments, the combustion product of diesel particulate matter is a soot oxidation product, e.g., CO, and the noted downstream NO_x adsorber is regenerated with the assistance of CO derived from the oxidation of the diesel particulate matter. The downstream NO_x adsorber is provided in sufficiently close proximity to the diesel particulate filter to maximize the probability that the CO will assist in regeneration of the NO_x adsorber. Preferably, the CO assists NO_x adsorber regeneration by releasing stored NO_x, for example according to the reaction Ba(NO₃)₂ + 3CO → BaCO₃ + 2NO + 2CO₂. Furthermore, the CO preferably assists in regeneration of the NO_x adsorber by reducing the released NO_x to benign N₂, for example according to the reaction NO + CO → 1/2N₂ + CO₂. Furthermore, the CO preferably assists in regeneration of the NO_x adsorber by oxidizing CO (either through one of the above two reactions, or by reaction with O₂ over the noble metal component of the NO_x adsorber according to CO + 1/2O₂ → CO₂) with substantial heat release. Close proximity of the particulate filter to the NO_x adsorber allows efficient utilization of this heat to assist regeneration of the filters and systems disclosed herein.

[0043] In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.

Claims

1. An exhaust aftertreatment filter for filtering engine exhaust flowing along an axial direction,
said filter (10) being composed of monolithic regenerable material and comprising an axially extending filter element (18) having wall segments extending axially between upstream and downstream ends,
said wall segments defining axial flow channels therebetween,
said wall segments being alternately sealed to each other by a first set of plugs (34) to define a first set of flow channels closed by said plugs (34) and having open downstream ends, and a second set of flow channels interdigitated with said first set of flow channels and having open upstream ends, said wall segments being alternately sealed to each other by a second set of plugs (36) closing said second set of flow channels,
said wall segments further define a third set of channels having open flow, said third set of channels having selected positions in said filter (10) for reducing back pressure on said filter during operation while maintaining filtering efficiency and/or
for reducing high temperature in said filter during operation while maintaining filtering efficiency
and/or for increasing velocity of exhaust flow through said filter during operation while maintaining filtering efficiency,
characterized in that
said wall segments further define a fourth set of flow channels having closed downstream ends and closed upstream ends, said fourth set of flow channels forming a peripheral ring in said filter.

2. The filter of claim 1, characterized in that
said channels of said third set represent at least about 1% of total channels in said filter and said maintained filtering efficiency is at least about 75%.

3. The filter according to any one of the preceding claims, characterized in that it further comprises a coating material along at least some of said wall segments defining said third set of flow channels,
wherein, preferably, said coating material comprises a catalytic agent for at least one reaction selected from the group consisting of 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; and 4C_xH_y + (4x+y)O₂ → (4x)CO₂ + (2y)H₂O, where x is an integer selected from 1-25 and y is an integer selected from 0-52.

4. The filter according to any one of the preceding claims, characterized in that
said wall segments defining said third set of flow channels have an average thickness greater than an average thickness of said wall segments defining said first set of flow channels or said wall segments defining said second set of flow channels.

5. The filter according to any one of the preceding claims, characterized in that
said wall segments defining said fourth set of flow channels have an average thickness greater than an average thickness of said wall segments defining said first set of flow channels or said wall segments defining said second set of flow channels and/or
said third set of flow channels are arranged in a ring adjacent to the peripheral ring formed by the fourth set of flow channels.

6. The filter according to any one of the preceding claims, characterized in that
said third set of flow channels are distributed in said filter in a gradient, said filter having an increasing concentration of open channels in sections located at peripheral positions in said filter as compared to sections located at central positions of said filter.

7. The filter according to any one of the preceding claims, characterized in that filter is composed of a ceramic material selected from the group consisting of cordierite, silicon carbide, mullite, and aluminum titanate.

8. An exhaust aftertreatment system for filtering engine exhaust flowing along an axial direction, said system comprising in series along said axial direction: a diesel oxidation catalyst, an exhaust aftertreatment filter according to any one of the preceding claims, and a second filter.

9. An exhaust aftertreatment system for filtering engine exhaust flowing along an axial direction, said system comprising at least a first and a second filter arranged in series along said axial direction, said first filter being positioned upstream of said second filter and having a lower filtration efficiency than said second filter, wherein at least one of said first and second filter is a filter according to any one of the claims 1 to 8.

10. The system of claim 9, characterized in that
said first filter is composed of said filtration material and/or said second filter is composed of said filtration material,
wherein, preferably, said first filter and said second filter are composed of a ceramic material selected from cordierite, silicon carbide, mullite, and aluminum titanate.

11. The system of claim 9 or 10, characterized in that
said first filter is composed of a first filtration material and said second filter is composed of a second filtration material that is different than said first filtration material,
wherein, preferably, said first filtration material has a larger pore diameter than said second filtration material and/or
said first filter has a cell density of greater than 46,5 per cm² (300 per square inch) and comprises flow through channels and/or
said second filter has a cell density of greater than 31 per cm² (200 per square inch).

12. The system of any one of the claims 9 to 11, characterized in that said first filter has a soot filtration efficiency of at least about 50% and said second filter has a soot filtration efficiency of at least about 90%, wherein, preferably, said first filter has a soot filtration efficiency of about 50-60%.

13. The system according to any one of the claims 9 to 12, characterized in that it further comprises a diesel oxidation catalyst element arranged in series with said first filter and said second filter along said axial direction, said diesel oxidation catalyst element being positioned upstream of said first filter and comprising a catalytic agent for at least one reaction selected from the group consisting of 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; and 4C_xH_y + (4x+y)O₂ → (4x)CO₂ + (2y)H₂O, where x is an integer selected from 1-25 and y is an integer selected from 0-52.

14. A method of manufacturing a modified exhaust aftertreatment filter according to any of claims 1-7, the method according to the invention comprising selecting and removing at least one plug of said first set of plugs and said second set of plugs to provide open flow in at least one channel of said modified filter,
said selected plug being located at a position in said unmodified filter whereby removing said plug reduces back pressure on said modified filter during operation while maintaining filtering efficiency and/or
said selected plug being located at a position in said unmodified filter which is subject to relatively high temperature during operation of said unmodified filter as
compared to a non-selected plug, thereby reducing said relatively high temperature during operation of said modified filter while maintaining filtering efficiency, and/or
said selected plug being located at a position in said unmodified filter where exhaust flow exhibits relatively low velocity during operation of said unmodified filter as compared to a position of a non-selected plug, thereby increasing said relatively low velocity during operation of said modified filter while maintaining filtering efficiency.

15. A modified exhaust aftertreatment filter for filtering engine exhaust prepared by the method of claim 14.

Ansprüche

1. Abgasnachbehandlungsfilter zum Filtern von in einer axialen Richtung strömendem Kraftmaschinenabgas,
wobei der Filter (10) aus regenerierbarem monolithischem Material aufgebaut ist und ein sich axial erstreckendes Filterelement (18) mit Wandsegmenten, die sich zwischen einem stromaufseitigen und einem stromabseitigen Ende axial erstrecken, enthält,
wobei die Wandsegmente zwischen sich axiale Strömungskanäle definieren,
wobei die Wandsegmente durch eine erste Menge von Stopfen (34) abwechselnd aneinander abgedichtet sind, um eine erste Menge von Strömungskanälen zu definieren, die durch die Stopfen (34) verschlossen sind und offene stromabseitige Enden haben, und um eine zweite Menge von Strömungskanälen zu definieren, die mit der ersten Menge von Strömungskanälen interdigital angeordnet sind und offene stromaufseitige Enden besitzen, wobei die Wandsegmente durch eine zweite Menge von Stopfen (36), die die zweite Menge von Strömungskanälen verschließen, abwechselnd aneinander abgedichtet sind,
wobei die Wandsegmente ferner eine dritte Menge von Kanälen mit offener Strömung definieren, wobei die dritte Menge von Kanälen in dem Filter (10) ausgewählte Positionen haben, um den Gegendruck auf den Filter während des Betriebs zu verringern, während der Filterungswirkungsgrad aufrechterhalten wird, und/oder um eine hohe Temperatur in dem Filter während des Betriebs zu verringern, während der Filterungswirkungsgrad aufrechterhalten wird; und/oder um die Geschwindigkeit der Abgasströmung durch den Filter während des Betriebs zu erhöhen, während der Filterungswirkungsgrad aufrechterhalten wird;
dadurch gekennzeichnet, dass
die Wandsegmente ferner eine vierte Menge von Strömungskanälen definieren, die geschlossene stromabseitige Enden und geschlossene stromaufseitige Enden besitzen, wobei die vierte Menge von Strömungskanälen in dem Filter einen Umfangsring bilden.

2. Filter nach Anspruch 1, dadurch gekennzeichnet, dass
die Kanäle der dritten Menge wenigstens etwa 1 % der gesamten Kanäle in dem Filter darstellen und der aufrechterhaltene Filterungswirkungsgrad wenigstens etwa 75 % beträgt.

3. Filter nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass er ferner ein Beschichtungsmaterial wenigstens längs einiger der Wandsegmente, die die dritte Menge von Strömungskanälen definieren, umfasst,
wobei das Beschichtungsmaterial vorzugsweise einen katalytischen Wirkstoff für wenigstens eine Reaktion enthält, die aus der Gruppe gewählt ist, die besteht aus 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; und 4C_xH_y + (4x + y)O₂ → (4x)CO₂ + (2y)H₂O, wobei x eine ganze Zahl im Bereich von 1-25 ist und y eine ganze Zahl im Bereich von 0-52 ist.

4. Filter nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass
die Wandsegmente, die die dritte Menge von Strömungskanälen definieren, eine durchschnittliche Dicke haben, die größer ist als eine durchschnittliche Dicke der Wandsegmente, die die erste Menge von Strömungskanälen definieren, oder der Wandsegmente, die die zweite Menge von Strömungskanälen definieren.

5. Filter nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass
die Wandsegmente, die die vierte Menge von Strömungskanälen definieren, eine durchschnittliche Dicke haben, die größer als eine durchschnittliche Dicke der Wandsegmente ist, die die erste Menge von Strömungskanälen definieren, oder der Wandsegmente, die die zweite Menge von Strömungskanälen definieren, und/oder
die dritte Menge von Strömungskanälen in einem Ring in der Nähe des Umfangsrings, der durch die vierte Menge von Strömungskanälen gebildet ist, angeordnet ist.

6. Filter nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass
die dritte Menge von Strömungskanälen in dem Filter in einem Gradienten verteilt sind, wobei der Filter im Vergleich zu Bereichen, die sich an Mittelpositionen des Filters befinden, in Bereichen, die sich an Umfangspositionen in dem Filter befinden, eine zunehmende Konzentration offener Kanäle besitzt.

7. Filter nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass
der Filter aus einem Keramikmaterial aufgebaut ist, das aus der Gruppe gewählt ist, die aus Cordierit, Siliciumcarbid, Mullit und Aluminiumtitanat besteht.

8. Abgasnachbehandlungssystem zum Filtern von in einer axialen Richtung strömendem Kraftmaschinenabgas, wobei das System in einer Reihe in der axialen Richtung Folgendes umfasst: einen Dieseloxidationskatalysator, einen Abgasnachbehandlungsfilter nach einem der vorhergehenden Ansprüche und einen zweiten Filter.

9. Abgasnachbehandlungssystem zum Filtern von in einer axialen Richtung strömendem Kraftmaschinenabgas, wobei das System wenigstens einen ersten und einen zweiten Filter, die in einer Reihe in der axialen Richtung angeordnet sind, umfasst, wobei der erste Filter stromaufseitig des zweiten Filters positioniert ist und einen niedrigeren Filterungswirkungsgrad als der zweite Filter hat, wobei der erste und/oder der zweite Filter ein Filter nach einem der Ansprüche 1 bis 8 sind.

10. System nach Anspruch 9, dadurch gekennzeichnet, dass
der erste Filter aus dem Filtermaterial aufgebaut ist und/oder der zweite Filter aus dem Filtermaterial aufgebaut ist,
wobei vorzugsweise der erste Filter und der zweite Filter aus einem Keramikmaterial aufgebaut sind, das aus Cordierit, Siliciumcarbid, Mullit und Aluminiumtitanat gewählt ist.

11. System nach Anspruch 9 oder 10, dadurch gekennzeichnet, dass
der erste Filter aus einem ersten Filtermaterial aufgebaut ist und der zweite Filter aus einem zweiten Filtermaterial, das von dem ersten Filtermaterial verschieden ist, aufgebaut ist,
wobei das erste Filtermaterial vorzugsweise einen größeren Porendurchmesser als das zweite Filtermaterial besitzt und/oder
der erste Filter eine Zellendichte größer als 46,5 pro cm² (300 pro Quadratzoll) besitzt und eine Strömung durch Kanäle aufweist und/oder
der zweite Filter eine Zellendichte größer als 31 pro cm² (200 pro Quadratzoll) besitzt.

12. System nach einem der Ansprüche 9 bis 11, dadurch gekennzeichnet, dass
der erste Filter einen Rußfilterungswirkungsgrad von wenigstens etwa 50 % besitzt und der zweite Filter einen Rußfilterungswirkungsgrad von wenigstens etwa 90 % besitzt, wobei vorzugsweise der erste Filter einen Rußfilterungswirkungsgrad von etwa 50-60 % besitzt.

13. System nach einem der Ansprüche 9 bis 12, dadurch gekennzeichnet, dass
es ferner ein Dieseloxidationskatalysatorelement umfasst, das in einer Reihe mit dem ersten Filter und dem zweiten Filter in der axialen Richtung angeordnet ist, wobei das Dieseloxidationskatalysatorelement stromaufseitig des ersten Elements positioniert ist und einen katalytischen Wirkstoff für wenigstens eine Reaktion umfasst, die aus der Gruppe gewählt ist, die besteht aus 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; und 4C_xH_y + (4x + y)O₂ → (4x)CO₂ + (2y)H₂O, wobei x eine ganze Zahl im Bereich von 1-25 ist und y eine ganze Zahl im Bereich von 0-52 ist.

14. Verfahren zum Herstellen eines modifizierten Abgasnachbehandlungsfilters nach einem der Ansprüche 1-7,
wobei das Verfahren gemäß der Erfindung Folgendes umfasst: Auswählen und Entfernen wenigstens eines Stopfens der ersten Menge von Stopfen und der zweiten Menge von Stopfen, um eine offene Strömung in wenigstens einem Kanal des modifizierten Filters bereitzustellen,
wobei sich der ausgewählte Stopfen an einer Position in dem nicht modifizierten Filter befindet, wobei das Entfernen des Stopfens den Gegendruck auf den modifizierten Filter während des Betriebs verringert, während der Filterungswirkungsgrad aufrechterhalten wird, und/oder
der ausgewählte Stopfen sich an einer Position in dem nicht modifizierten Filter befindet, die im Vergleich zu einem nicht ausgewählten Stopfen einer verhältnismäßig hohen Temperatur während des Betriebs des nicht modifizierten Filters unterworfen ist, wodurch die verhältnismäßig hohe Temperatur während des Betriebs des modifizierten Filters verringert wird, während der Filterungswirkungsgrad aufrechterhalten wird, und/oder
der ausgewählte Stopfen sich an einer Position in dem nicht modifizierten Filter befindet, wo die Abgasströmung im Vergleich zu einer Position eines nicht ausgewählten Stopfens eine verhältnismäßig niedrige Geschwindigkeit während des Betriebs des nicht modifizierten Filters zeigt, wodurch die verhältnismäßig niedrige Geschwindigkeit während des Betriebs des modifizierten Filters erhöht wird, während der Filterungswirkungsgrad aufrechterhalten wird.

15. Modifizierter Abgasnachbehandlungsfilter zum Filtern von Kraftmaschinenabgas, der durch das Verfahren nach Anspruch 14 bereitgestellt wird.

Revendications

1. Filtre de post-traitement de gaz d'échappement destiné au filtrage des gaz d'échappement d'un moteur s'écoulant le long d'une direction axiale,
ledit filtre (10) étant composé de matériau monolithique régénérable et comprenant un élément de filtre s'étendant axialement (18) qui comporte des segments de paroi s'étendant axialement entre les extrémités amont et aval,
lesdits segments de paroi définissant entre eux des canaux d'écoulement axiaux,
lesdits segments de paroi étant alternativement scellés l'un par rapport à l'autre par un premier ensemble de bouchons (34) afin de définir un premier ensemble de canaux d'écoulement fermés par lesdits bouchons (34) et ayant des extrémités aval ouvertes, et un deuxième ensemble de canaux d'écoulement alternant avec ledit premier ensemble de canaux d'écoulement et ayant des extrémités amont ouvertes, lesdits segments de paroi étant alternativement scellés l'un par rapport à l'autre par un deuxième ensemble de bouchons (36) fermant ledit deuxième ensemble de canaux d'écoulement, lesdits segments de paroi définissent en outre un troisième ensemble de canaux ayant un écoulement ouvert, ledit troisième ensemble de canaux occupant des positions sélectionnées dans ledit filtre (10),
pour réduire la contrepression sur ledit filtre pendant le fonctionnement tout en maintenant l'efficacité du filtrage, et/ou
pour réduire la haute température dans ledit filtre pendant le fonctionnement tout en maintenant l'efficacité du filtrage, et/ou
pour augmenter la vitesse de l'écoulement des gaz d'échappement à travers ledit filtre pendant le fonctionnement tout en maintenant l'efficacité du filtrage,
caractérisé en ce que lesdits segments de paroi définissent en outre un quatrième ensemble de canaux d'écoulement ayant des extrémités aval fermées et des extrémités amont fermées, ledit quatrième ensemble de canaux d'écoulement formant un anneau périphérique dans ledit filtre.

2. Filtre selon la revendication 1, caractérisé en ce que lesdits canaux dudit troisième ensemble représentent au moins environ 1% des canaux totaux dans ledit filtre et ladite efficacité de filtrage maintenue est d'au moins environ 75 %.

3. Filtre selon l'une quelconque des revendications précédentes, caractérisé en ce qu'il comprend en outre un matériau de revêtement le long d'au moins certains desdits segments de paroi définissant ledit troisième ensemble de canaux d'écoulement,
dans lequel de préférence ledit matériau de revêtement comprend un agent catalytique pour au moins une réaction sélectionnée dans le groupe composé de 2CO + O₂ → 2CO₂: 2NO + O₂ → 2NO₂; et 4C_xH_y + (4x+y)O₂ → (4x))CO₂ + (2y)H₂O, où x est un entier sélectionné de 1 à 25 et y est un entier sélectionné de 0 à 52.

4. Filtre selon l'une quelconque des revendications précédentes, caractérisé en ce que lesdits segments de paroi définissant ledit troisième ensemble de canaux d'écoulement présentent une épaisseur moyenne plus grande qu'une épaisseur moyenne desdits segments de paroi définissant ledit premier ensemble de canaux d'écoulement ou desdits segments de paroi définissant ledit deuxième ensemble de canaux d'écoulement.

5. Filtre selon l'une quelconque des revendications précédentes, caractérisé en ce que lesdits segments de paroi définissant ledit quatrième ensemble de canaux d'écoulement présentent une épaisseur moyenne plus grande qu'une épaisseur moyenne desdits segments de paroi définissant ledit premier ensemble de canaux d'écoulement ou desdits segments de paroi définissant ledit deuxième ensemble de canaux d'écoulement, et/ou ledit troisième ensemble de canaux d'écoulement est agencé en un anneau adjacent à l'anneau périphérique formé par ledit quatrième ensemble de canaux d'écoulement.

6. Filtre selon l'une quelconque des revendications précédentes, caractérisé en ce que ledit troisième ensemble de canaux d'écoulement est distribué dans ledit filtre en un gradient, ledit filtre présentant une concentration croissante de canaux ouverts dans des sections situées à des positions périphériques dans ledit filtre par comparaison avec des sections situées à des positions centrales dudit filtre.

7. Filtre selon l'une quelconque des revendications précédentes, caractérisé en ce que le filtre est composé d'un matériau céramique sélectionné dans le groupe composé de la cordiérite, du carbure de silicium, de la mullite et du titanate d'aluminium.

8. Système de post-traitement de gaz d'échappement destiné au filtrage des gaz d'échappement d'un moteur s'écoulant le long d'une direction axiale, ledit système comprenant en série le long de ladite direction axiale: un catalyseur d'oxydation diesel, un filtre de post-traitement de gaz d'échappement selon l'une quelconque des revendications précédentes, et un deuxième filtre.

9. Système de post-traitement destiné au filtrage des gaz d'échappement d'un moteur s'écoulant le long d'une direction axiale, ledit système comprenant au moins un premier et un deuxième filtres agencés en série le long de ladite direction axiale, ledit premier filtre étant positionné en amont dudit deuxième filtre et présentant une efficacité de filtrage inférieure à celle du deuxième filtre, dans lequel au moins un dudit premier filtre et dudit deuxième filtre est un filtre selon l'une quelconque des revendications 1 à 8.

10. Système selon la revendication 9, caractérisé en ce que ledit premier filtre est composé dudit matériau de filtrage et/ou ledit deuxième filtre est composé dudit matériau de filtrage, dans lequel de préférence ledit premier filtre et ledit deuxième filtre sont composés d'un matériau céramique sélectionné parmi la cordiérite, le carbure de silicium, la mullite, et le titanate d'aluminium.

11. Système selon la revendication 9 ou 10,
caractérisé en ce que
ledit premier filtre est composé d'un premier matériau de filtrage et ledit deuxième filtre est composé d'un deuxième matériau de filtrage qui est différent dudit premier matériau de filtrage,
dans lequel de préférence ledit premier matériau de filtrage présente un plus grand diamètre de pores que ledit deuxième matériau de filtrage, et/ou ledit premier filtre présente une densité de cellules de plus de 46,5 par cm² (300 par pouce carré) et comporte des canaux d'écoulement traversants et/ou ledit deuxième filtre présente une densité de cellules de plus de 31 par cm² (200 par pouce carré).

12. Système selon l'une quelconque des revendications 9 à 11, caractérisé en ce que ledit premier filtre présente une efficacité de filtrage de suie d'au moins environ 50 % et ledit deuxième filtre présente une efficacité de filtrage de suie d'au moins environ 90 %, dans lequel de préférence ledit premier filtre présente une efficacité de filtrage de suie d'environ 50 - 60 %.

13. Système selon l'une quelconque des revendications 9 à 12, caractérisé en ce qu'il comprend en outre un élément de catalyseur d'oxydation diesel agencé en série avec ledit premier filtre et ledit deuxième filtre dans ladite direction axiale, ledit élément de catalyseur d'oxydation diesel étant positionné en amont dudit premier filtre et comprenant un agent catalytique pour au moins une réaction sélectionnée dans le groupe composé de 2CO + O₂ → 2CO₂; 2NO + O₂ → 2NO₂; et 4C_xH_y + (4x+y)O₂ → (4x)CO₂ + (2y)H₂O, où x est un entier sélectionné de 1 à 25 et y est un entier sélectionné de 0 à 52.

14. Procédé de fabrication d'un filtre modifié de post-traitement de gaz d'échappement selon l'une quelconque des revendications 1 à 7, le procédé selon l'invention comprenant la sélection et l'enlèvement d'au moins un bouchon dudit premier ensemble de bouchons et dudit deuxième ensemble de bouchons pour produire un écoulement ouvert dans au moins un canal dudit filtre modifié,
ledit bouchon sélectionné étant situé à une position dans ledit filtre non modifié, pour laquelle l'enlèvement dudit bouchon réduit la contrepression sur ledit filtre modifié pendant le fonctionnement tout en maintenant l'efficacité de filtrage, et/ou ledit bouchon sélectionné étant situé à une position dans ledit filtre non modifié qui est soumise à une température relativement élevée pendant le fonctionnement dudit filtre non modifié par comparaison avec un bouchon non sélectionné, réduisant ainsi ladite température relativement élevée pendant le fonctionnement dudit filtre modifié tout en maintenant l'efficacité de filtrage, et/ou
ledit bouchon sélectionné étant situé à une position dans ledit filtre non modifié où l'écoulement de gaz d'échappement présente une vitesse relativement faible pendant le fonctionnement dudit filtre non modifié par comparaison avec une position d'un bouchon non sélectionné, augmentant ainsi ladite vitesse relativement faible pendant le fonctionnement dudit filtre modifié tout en maintenant l'efficacité de filtrage.

15. Filtre modifié de post-traitement de gaz d'échappement destiné au filtrage des gaz d'échappement d'un moteur préparé par le procédé de la revendication 14.

Drawing